1. Field of the Invention
The present invention relates generally to check valve systems that are typically required by industry standards for coiled tubing well interventions. More specifically, the present invention concerns a check valve system having the capability of being controlled by selective mechanical cycling movement or flow responsive movement of tool components to permit controlled selection of a direct circulating flow mode or a reverse circulating flow mode, thus permitting the check valve tool to assist in the performance of servicing operations such as sand cleanout or well flow up a section of, or the entire, coiled tubing string.
2. Description of Related Art
It is a safety standard in coiled tubing operations to have a check valve with a  minimum of two pressure barriers in the tool string. In many coiled tubing operations, such as fracturing and well cleanout operations, it is desirable to reverse circulate through the coiled tubing. Reverse circulating (flowing upwardly within the passage of the coiled tubing, instead of downwardly) is not possible when conventional dual check valves are employed.